Despite advances in CF research, we still do not understand the pathogenesis of airways disease. A major mpediment to progress is lack of a CF animal model other than the mouse. Although CF mice have been produced, they do not develop the airway disease typically found in humans. Therefore, we developed a pig with a targeted disruption of the CFTR gene. We chose the pig because its lungs share many anatomical, histological, biochemical, and physiologic features with human lungs. In this project, we take the unique opportunity to learn how loss of CFTR alters airway epithelial function in this new CF model. Several hypotheses about the pathogenesis of CF airway disease center on defective airway epithelial electrolyte transport and abnormal airway surface liquid volume and composition. These topics are the main focus of our application. Through collaborations with the other projects in the Program, we will discern how altered epithelial function relates to inflammation and infection, clinical hallmarks of the disease. We concentrate on early postnatal and young pigs because there is a critical lack of information about the human CF lung during this time, and yet this is precisely when loss of CFTR initiates disease. Specific Aim 1. Does loss of CFTR alter the function of porcine airway epithelia? We will learn how lack of CFTR changes ion transport in vivo using measurements of transepithelial voltage, in vitro using cultures of differentiated pig airway epithelia, in freshly excised airway epithelia, and in the distal airways of the lung. We will also learn whether apical Na+ channel and alternative CI channel activities are increased, and how their function relates to the clinical phenotype. Specific Aim 2. Does loss of porcine CFTR change the airway surface liquid (ASL)? Much controversy surrounds hypotheses about how lack of CFTR affects ASL. Does it reduce ASL volume? Does it change ASL ion concentrations? Is ASL pH altered? Do changes occur both in vitro and in vivo? We will answer these questions using several independent methods. By studying both young pigs and animals after they develop inflammation and/or infection, we will discover how these processes change this critical liquid. Specific Aim 3. Does loss of CFTR disrupt mucociliary transport? Lack of CFTR might cause defective mucociliary transport (MCT) thereby initiating airway disease. Alternatively, other factors might initiate the disease process, and then secondary defects in MCT might worsen airways disease. Current data do not allow us to discriminate between these or other hypotheses. Here, we test the hypothesis that loss of CFTR disrupts normal MCT in vitro and in vivo. These studies will provide new insights into both CF pathogenesis and pathophysiology and thereby accelerate the discovery of novel therapies for this lethal disease.